Aberrant folding of proteins is a feature comnnon to many neurodegenerative diseases, including prion disease, Huntington's disease (HD), Alzheimer's disease, and others. Misfolded proteins may adopt several distinct tertiary and quaternary conformations, both in terms of their stable, end states, and in terms of meta-stable intermediate states they acquire as they progress from monomers to large aggregated protein deposits in the brain. Identification of specific protein conformations involved in disease processes is lacking for many neurodegenerative diseases, although we have made progress in this regard for prion disease during the mentored phase ofthis award (Colby et.al., PNAS 2009; Colby etal., PLoS Pathog. 2010). We have begun to elucidate the manner in which biophysical properties of misfolded proteins correlate to and even directly result in specific disease phenotypes. in HD however, the role of misfolded proteins in pathogenesis is controversial and much work remains to be done to establish the conformational basis of this disease. In the independent phase of this award, we will apply the same approaches we have leamed over the past several years studying prion disease to HD in order to identify specific conformations ofthe huntingtin protein that result in neurodegeneration. Using peptides, recombinant protein, and misfolded proteins isolated from laboratory animal models and cell culture models, as well as HD patients, we will assess the extent to which the huntingtin protein is capable of acquiring diverse conformations. We will then determine if any of these conformations are capable of initiating neural death or dysfunction in cell and animal models. In a complementary approach, we will also devielop a technique for detecting misfolded huntingtin based on the propensity of misfolded proteins to nucleate or 'seed' amyloid formation. An analogous assay for detecting prions had femtogram sensitivity (Colby et. al., PNAS, 2007). The ability to sensitively detect misfolded huntingtin will enable us to identify its presence much earlier in disease progression than is currently possible. A better understanding ofthe molecular basis of Huntington's disease and related neurodegenerative disorders shall aid substantially in the search for a cure.